1. Field of the Invention
Embodiments of the invention generally provide a substrate support utilized in semiconductor processing and a method of fabricating the same.
2. Description of the Background Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Generally, flat panels comprise two glass plates having a layer of liquid crystal material sandwiched therebetween. At least one of the glass plates includes at least one conductive film disposed thereon that is coupled to a power supply. Power supplied to the conductive film from the power supply changes the orientation of the crystal material, creating a pattern such as text or graphics seen on the display. One fabrication process frequently used to produce flat panels is plasma enhanced chemical vapor deposition (PECVD).
Plasma enhanced chemical vapor deposition is generally employed to deposit thin films on a substrate such as a flat panel or semiconductor wafer. Plasma enhanced chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber that contains a substrate. The precursor gas is typically directed through a distribution plate situated near the top of the chamber. The precursor gas in the chamber is energized (e.g., excited) into a plasma by applying RF power to the chamber from one or more RF sources coupled to the chamber. The excited gas reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. In applications where the substrate receives a layer of low temperature polysilicon, the substrate support may be heated in excess of 400 degrees Celsius. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
Generally, the substrate support utilized to process flat panel displays are large, often exceeding 550 mmxc3x97650 mm. The substrate supports for high temperature use typically are casted, encapsulating one or more heating elements and thermocouples in an aluminum body. Due to the size of the substrate support, one or more reinforcing members are generally disposed within the substrate support to improve the substrate support""s stiffness and performance at elevated operating temperatures (i.e., in excess of 350 degrees Celsius and approaching 500 degrees Celsius). Although substrate supports configured in this manner have demonstrated good processing performance, manufacturing supports has proven difficult.
One problem in providing a robust substrate support is that the reinforcing member may occasionally displace, deform and sometimes break during the casting process. The reinforcing member typically includes portions that are unsupported in the pre-cast state of the substrate support. After assembling the reinforcing member, the heating elements and thermocouples into a subassembly, the subassembly is supported in a mold and encapsulated with molten aluminum. Conventional presses used in the casting process typically have one or twin rams that provide up to about 500 tons of pressure that works not whole area of cast surface but local area flowing the molten aluminum around the subassembly disposed in the substrate support mold. In this case, there is always nonuniformity of pressure working on the molten aluminum. Occasionally, this nonuniformity of the weight and pressure of the aluminum flowing in the mold during the casting process causes the reinforcing member to displacement, deformation and sometimes fracture. Additionally, this casting process results in undesirable heterogeneous grain size of aluminum cast. Furthermore, such pressures stress the substrate support up to about 28 MPa, which is not enough to get a desired uniform micro-grain size within the aluminum cast.
Another problem with substrate support formed using this molding process is the lack of integrity of the aluminum where the flow of molten aluminum comes back together on the side of the substrate support furthest from the molten aluminum source. As a substantial amount of aluminum and time is needed to encapsulate the heating elements, thermocouples and reinforcing members, the flow of aluminum may cool causing a seam to be created where the leading edges of the aluminum flow merges under the subassembly at less than acceptable temperatures.
Depending on the temperature of the aluminum when the seam is formed, the seam may become a source of a variety of defects. For example, vacuum leaks may propagate through the seam between the interior of the chamber and the environment surrounding the chamber. Vacuum leakage may degrade process performance and may lead to poor heater performance that contributes to pre-mature heater failure. Moreover, thermal cycling of the substrate support may cause the substrate support to fracture along the seam, thereby causing failure and possible release of particulates into the chamber environment.
As the cost of materials and manufacturing the substrate support is great, failure of the substrate support is highly undesirable. Additionally, if the substrate support fails during processing, a substrate supported thereon may be damaged. This can occur after a substantial number of processing steps have been preformed thereon, thus resulting in the expensive loss of the substrate support. Moreover, replacing a damaged support in the process chamber creates a costly loss of substrate throughput while the process chamber is idled during replacement or repair of the substrate support. Moreover, as the size of the next generation substrate supports are increased to accommodate substrates in excess of 1.44 square meters at operating temperatures approaching 500 degrees Celsius, the aforementioned problems become increasingly important to resolve.
Therefore, there is a need for an improved substrate support.
Generally, a substrate support and method of fabricating the same are provided. In one embodiment, a method of fabricating a substrate support includes the steps of assembling a subassembly comprising a first reinforcing member and a heating element, supporting the subassembly at least 40mm from a bottom of a mold, encapsulating the supported subassembly with molten aluminum, and applying pressure to the molten aluminum.
In another embodiment, a method of fabricating a substrate support includes the steps of a method of fabrication includes assembling a subassembly comprising a stud disposed through a heating element sandwiched between a first reinforcing member and a second reinforcing member, supporting the subassembly above a bottom of a mold, encapsulating the subassembly disposed in the mold with molten aluminum to form a casting, forming a hole in the casting by removing at least a portion of the stud, and disposing a plug in at least a portion of the hole.
In another aspect of the invention, a substrate support is provided. In one embodiment, the substrate support includes at least a first reinforcing member and a heating element disposed within a cast aluminum body. At least one hole is formed in the aluminum body between an outer surface and at least the heating element or the reinforcing member. A plug is disposed in the hole between the outer surface and the heating element or the reinforcing member. In another embodiment, the hole houses a stud during casting that maintains the heating element and the reinforcing member in a spaced-apart relation and is at least partially removed from the hole before insertion of the plug.